One common method for printing images on a receiver material is referred to as electrophotography. The production of black-and-white or color images using electrophotography generally includes the producing a latent electrostatic image by uniformly charging a dielectric member such as a photoconductive substance, and then discharging selected areas of the uniform charge to yield an imagewise electrostatic charge pattern. Such discharge is generally accomplished by exposing the uniformly charged dielectric member to actinic radiation provided by selectively activating particular light sources in an LED array or a laser device directed at the dielectric member. After the imagewise charge pattern is formed, it is “developed” into a visible image using pigmented or non-pigmented marking particles (generally referred to as “toner particles”) by either using the charge area development (CAD) or the discharge area development (DAD) method that have an opposite charge to the dielectric member and are brought into the vicinity of the dielectric member so as to be attracted to the imagewise charge pattern.
Thereafter, a suitable receiver material (for example, a cut sheet of plain bond paper) is brought into juxtaposition with the toner image developed with the toner particles in accordance with the imagewise charge pattern on the dielectric member, either directly or using an intermediate transfer member. A suitable electric field is applied to transfer the toner particles to the receiver material in the imagewise pattern to form the desired print image on the receiver material. The receiver material is then removed from its operative association with the dielectric member and subjected to suitable heat or pressure or both heat and pressure to permanently fix (also known as fusing) the toner image (containing toner particles) to form the desired image on the receiver material.
Plural toner particle images of, for example, different color toner particles respectively, can be overlaid with multiple toner transfers to the receiver material, followed by fixing of all toner particles to form a multi-color image in the receiver material. Toners that are used in this fashion to prepare multi-color images are generally Cyan (C), Yellow (Y), Magenta (M), and Black (K) toners containing appropriate dyes or pigments to provide the desired colors or tones.
It is also known to use special spot toners to provide additional colors that cannot be obtained by simply mixing the four “primary” toners. An example is a specially designed toner that provides a color spot or pearlescent effect.
With the improved print image quality that is achieved with the more recent electrophotographic technology, print providers and customers alike have been looking for ways to expand the use of images prepared using electrophotography. Printing processes serve not only to reproduce and transmit objective information but also to convey esthetic impressions, for example, for glossy books or pictorial advertizing.
The desire to provide fluorescing effects has existed for several decades and U.S. Pat. No. 3,713,861 (Sharp et al.) describes coating a fluorescent material over a document image.
Many color images cannot be reproduced using the traditional CYMK color toners. Specifically, fluorescing colors or tones cannot be readily reproduced using the CYMK color toner set. It has been proposed to incorporate fluorescing pigments or dyes into liquid toner particles as described in U.S. Pat. No. 5,105,451 (Lubinsky et al.).
U.S. Patent Application Publication 2010/0164218 (Schulze-Hagenest et al.) describes the use of substantially clear (colorless) fluorescent toner particles in printing methods over color toner images. Such clear fluorescent toner particles can be used for security purposes since they are not colored except when excited with appropriate light. Other invisible fluorescent pigments for toner images are described in U.S. Pat. No. 6,664,017 (Patel et al.).
Printing processes for providing one or more color toner images are known, but it is also desired that fluorescing effects can also be provided for any type of color toner image in order to expand the color gamut while using conventional non-fluorescing color toners. However, it has been difficult to properly design desired fluorescing effects using known fluorescing colorants (dyes and pigments) as many of them are very sensitive to the illuminating radiation. Further, the color reproduction using fluorescing color toners produces unrealistically “bright” colors for most objects. This is usually an undesirable effect.
When illuminating light has some portion of the electromagnetic spectrum that is absorbed by fluorescing colorants that emit at a different wavelength, the overall resulting emissions are very “bright” and may overwhelm the non-fluorescing traditional colors in the color toner images. This again results in unrealistic images. Other illuminating light may not have substantial radiation that is absorbed, and the resulting emission from the fluorescing colorants is quite different. It is undesirable to have the fluorescing effects depend upon the illuminating light since constantly changing emissions and effects would reduce consistency in the resulting color image tone and discourage customers from using the fluorescing effects. This is often referred to as illuminant sensitivity and is not a desirable effect.
Typical electrophotographic toners and imaging procedures offer a limited color gamut (or ability to provide varying colors using the same set of toner particles). This is especially true in the yellow portion of the color space because of the inability of typical yellow hues to replicate some light and pale yellow hues, green hues, and orange hues.
While it is known to use fluorescent colors (for example, fluorescent toner particles) can be used to provide vibrant and colorful images, as suggested in the publications cited above. Copending and commonly assigned U.S. Ser. No. 13/462,133 (filed May 2, 2012 by Tyagi and Granica) describes unique fluorescing yellow polymeric toner particles and their use to provide fluorescent highlights in electrophotographic toner images. Various fluorescing polymeric toner particles are also described in various imaging methods in copending and commonly assigned U.S. Ser. No. 13/462,182 (filed May 2, 2012 by Tyagi, Granica, and Kuo), Ser. No. 13/462,155 (filed May 2, 2012 by Tyagi and Granica), and Ser. No. 13/462,111 (filed May 2, 2012 by Tyagi, Lofftus, Granica, and Allen).
While such fluorescing yellow polymeric toner particles are useful to provide enhanced or highlighted toner images, there remains a need to expand the possible color gamut with fluorescing effects and to provide more natural or realistic colors used in some printing jobs, especially in 4 color CYMK imaging processes.